1. Field of the Invention
The present invention relates generally to substrates for mounting electronic components and more particularly to a substrate of a case for packaging chip-type electronic components. The present invention also relates to a piezoelectric resonance component including such a substrate.
2. Description of the Related Art
Conventionally, various chip-type piezoelectric resonance components including piezoelectric elements are known. Because the piezoelectric vibrating part in the piezoelectric resonator vibrates, the packaging of the piezoelectric resonator must be done in a manner that does not prevent or hinder the vibration.
FIG. 6 is an assembly view showing an example of a conventional chip-type piezoelectric resonance component.
This chip-type piezoelectric resonance component includes a substrate 51 made of an insulative ceramic such as alumina. On the upper surface of the substrate 51, electrodes 52 to 54 for achieving external electrical connection are provided. Also on the upper surface of the substrate 51, a rectangular-frame-shaped insulative glass layer 55 is disposed.
On the substrate 51, a capacitor 57 is bonded via a conductive adhesive 56. On the capacitor 57, a piezoelectric resonator 58, which vibrates in a thickness shear mode, is bonded by conductive adhesives (not shown).
A metal cap 59 is bonded on the upper surface of the substrate 51 by using an adhesive 60 so as to cover the layered structure including the capacitor 57 and the piezoelectric resonator 58.
The rectangular-frame-shaped insulative glass layer 55 prevents a short-circuit between the metal cap 59 and the electrodes 52 to 54.
FIG. 7 is an assembly view which shows another example of a conventional chip-type piezoelectric resonance component. This piezoelectric resonance component includes a substrate 61 having a dielectric body. The substrate 61 including the dielectric body has three capacitor electrodes, which constitute a three-terminal capacitor. Electrodes 62 and 63 are provided on the upper surface of the substrate 61 and an electrode 64 is disposed on the side surface of the substrate 61. The three-terminal capacitor is defined by the electrodes 62 to 64.
On the upper surface of the substrate 61, a piezoelectric resonator 66 which vibrates in a thickness shear mode is fixed by a conductive adhesive 65. A metal cap 67 is bonded on the upper surface of the base substrate 61 so as to cover the piezoelectric resonator 66. In this example, in order to reliably prevent a short-circuit between the metal cap 67 and the electrodes 62 and 63, an insulator 69 is applied to the metal cap 67 in advance. After hardening, the metal cap 67 is bonded to the substrate 61 via an insulative adhesive 68.
As is apparent from the above, when the substrates 51 and 61 are bonded to the metal caps 59 and 67, respectively, a very difficult and cumbersome process for securing the insulation between the metal cap 59 and the electrodes 52 to 54 provided on the substrate 51, and for securing the insulation between the metal cap 67 and the electrodes 62 and 63 provided on the substrate 61 must be included in the manufacturing process of the conventional piezoelectric resonance components.
With respect to the chip-type piezoelectric resonance component shown in FIG. 6, when the electrodes 52 to 54 are formed by applying and baking a conductive paste after the substrate 51 made of alumina is baked, the baking process is repeated in order to bake the conductive paste, and, furthermore, in order to form the insulative glass layer 55 on the top thereof, insulative glass must be applied thereon and baked again. Because of these extremely cumbersome steps, the cost of the conventional piezoelectric resonance components is very high.
As for the chip-type piezoelectric resonance component shown in FIG. 7, an insulative resin 69 is applied to the metal cap 67 in advance and is hardened thereon. However, since the metal cap 67 is normally formed by deep-drawing a metal plate, the flatness at the opening edge thereof is not satisfactory. Consequently, it becomes extremely difficult to apply the insulative resin 69 on the opening edge of the metal cap 67 in an even manner. It also becomes difficult to obtain a seal between the substrate 61 and the metal cap 67.
As is apparent from the above description, in the manufacture of the chip-type piezoelectric resonance components using metal caps, it is necessary to perform the steps of forming the insulative glass layer 55 on the substrate 51 and applying the insulative resin 69.
In order to overcome the problems described above, preferred embodiments of the present invention provide a substrate on which electric components are mounted and a chip-type piezoelectric resonance component including such a substrate.
The substrate according to preferred embodiments of the present invention provides a simplified structure for preventing a short-circuit between the metal cap and the electrodes on the substrate, facilitates attachment of the metal cap to the substrate, and greatly improves the sealing performance of the space enclosed by the substrate and the metal cap.
A substrate according to a preferred embodiment of the present invention includes a substrate body layer, a plurality of electrodes disposed on the substrate body layer, and a first glass-ceramic layer arranged so as to cover a portion of the electrode disposed on the substrate body layer.
Preferably, the substrate further includes a second glass-ceramic layer disposed on the lower surface of the substrate body layer.
The first and second glass ceramic layers may include one of anorthite-type crystallized glass, forsterite-type crystallized glass, celsian-type crystallized glass, a composite including a ceramic powder and one the above crystallized glasses, and a composite including a ceramic powder and non-crystallized glass.
A piezoelectric resonance component according to another preferred embodiment of the present invention includes the substrate of the above-described preferred embodiment of the present invention, a piezoelectric resonator mounted on the substrate, and a conductive cap bonded to the first glass ceramic layer of the substrate, so as to cover the piezoelectric resonator.
Preferably, the substrate body layer of the substrate includes a dielectric body and a plurality of capacitor electrodes arranged to define a capacitor in the substrate body layer.
Preferably, the first glass-ceramic layer disposed on the upper surface of the substrate has a substantially rectangular-frame shaped configuration.
Preferably, the piezoelectric resonance component is a piezoelectric oscillator.
Because the first glass ceramic layer is disposed on the substrate main body so as to cover a portion of the electrodes, when the substrate body layer includes a dielectric ceramic or an insulative ceramic, the substrate body layer and the glass ceramic layer can be baked at the same time, thus reducing the manufacturing cost of the substrate.
Furthermore, because the upper surface of the glass ceramic layer has excellent flatness, when the metal cap is bonded thereon, the space enclosed by the metal cap and the substrate is tightly sealed.
When the second glass ceramic layer is disposed on the lower surface of the substrate body layer, mechanical strength of the substrate is greatly improved by the second glass ceramic layer. Thus, the reliability of the electronic components using the substrates of various preferred embodiments of the present invention is greatly improved.
When anorthite-type crystallized glass or forsterite-type crystallized is used in the first or second glass layers or both, these crystallized glasses have lower thermal expansion coefficients compared to alumina. Thus, when the metal cap is bonded thereon, the thermal expansion coefficient difference between the metal cap and the substrate is small, and an electronic component having superior thermal stress properties can be obtained.
In the piezoelectric resonance component according to a preferred embodiment of the present invention, a piezoelectric resonator is mounted on the substrate, and the conductive cap is bonded to the glass ceramic layer of the substrate so as to cover the piezoelectric resonator. Thus, the conductive cap can be firmly bonded to the substrate by using an insulative adhesive or other suitable material, and the substrate, as described above, is manufactured at lower cost and has superior mechanical strength. The space enclosed by the substrate and the conductive cap can be tightly sealed, and a highly reliable piezoelectric resonance component can be obtained.
In the piezoelectric resonance component of preferred embodiments of the present invention, when the substrate body layer of the substrate is made of a dielectric body and at least a pair of capacitor electrodes for constituting a capacitor are disposed on the substrate body layer, the capacitor is included in the substrate body layer. Thus, a built-in capacitor type piezoelectric resonance component can be provided.
When the first glass ceramic layer provided on the upper surface of the substrate has a substantially rectangular-frame shaped configuration, by aligning and bonding the substantially rectangular-frame shaped first glass ceramic layer and the opening edge of the conductive cap, the piezoelectric resonator can be fixed in the space surrounded by the first glass ceramic layer. Thus, a piezoelectric resonance component having superior sealing effects can be obtained.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments with reference to the attached drawings.